Definitely some trip-hop, which was, along with grunge, one of the most signature styles from the 90’s. But don’t limit yourself to **Massive Attack ** (as seminal as they were): other key artists are **The Sneaker Pimps ** and Morcheeba (mostly the half-minute intros, and the first 100 seconds of “Big Calm”). You might find use for White Town’s “Theme for an Early Evening American Sitcom,” 2:14 of instrumental synth-plus-marimbas cheesiness (and not a bit trip-hoppy).
Selections from the lounge revival of the mid-late '90’s: **Combustible Edison **'s work is a good starting point. I don’t have any on hand to refer to, but I remember it as being probably at least half-instrumental.
Pavement. One of the most instantly identifiably “90’s” bands of all (Nirvana probably earns the #1 spot.) Not many instrumentals, but lots of short chunks of good intro guitar strumming, etc., if you’ve got a small gap to fill.
Brit pop. The best band in this category was Blur, and their best-known LP in this country was Parklife. Instrumental track #7 (“The Debt Collector”) is an easy-going retro charmer, with oompa-oompa trombone, calliope-like sounds (melodica?), and saxophones. As for the rest, you’ll have to do the sampling (and loop?) the intros and such from the pop songs: the first 24 seconds of “London Loves,” for a classic, bouncy electronica-inflected pop sound; the first 36 seconds of “Clover Over Dover,” for a sprightly, cheerful, shimmery pop background; the first 53 seconds of “Lot 105” for a mellotron-and-cheesy-drum-synth minimalist track (that does build, a bit) that’s both retro and impossibly cute. And most recognizably, the first 31 seconds of “Girls and Boys,” Blur’s big hit at the time.
Arty jangle-pop. Sure, this sub-genre will forever be associated with the 80’s, with seminal albums like Crazy Rhythms by The Feelies. But the 90’s also saw some good stuff in this vein, like The Glands’s “Two Dollar Wine,” revisited in an instrumental reprise, “Two Dollar Reprise” on their debut LP Double Thriller [1998] (which also lists the shimmery instrumental “Sunshine Happiness”). Their 2000 LP, eponymously titled The Glands, was a much stronger work overall, but is better categorized in the shoegazer style. (With its obvious nods to Pavement, Suede and My Bloody Valentine, it also sounds like a time capsule of 90’s alternative-shoegazer rock.) It includes the 43-second instrumental “Swim - Prelude,” but you might find use for the 38-second mellow, hazy [or simply stoned?] intro to “Mayflower,” the jauntier 30-second intro to “I Can See My House from Here,” or the tranquil first 35 seconds of “Fortress”.
Another neat-o sub-genre of the 90’s was the revival of surf rock. The alterna-and-surf-rock-oriented (and all-instrumental) **Shadowy Men On a Shadowy Planet ** is best known for their theme for *The Kids In the Hall * TV show, but all their work is more or less on that level, quality-wise. (Try the LP Sport Fishin’ [1993], which was recorded by Steve Albini and must rank as one of the lost musical gems of the 90’s.) The other key all-instrumental surf-rock 90’s band is Man Or Astro-Man?, whose shtick marries surf-rock with '50’s-style sci-fi and monster-movie references (and Tesla coils, etc. for their stage show). (If MOA-M didn’t get to do the theme for MST3K, they should have.) You can also glean some good instrumental surf-rock from the eclectic Southern Culture On the Skids, esp. their wonderful debut LP Dirt Track Date [1995] – track #4, “Skullbucket” (the other instrumentals on that album are the Tiki-party-friendly “Make Mayan a Hawaiian” and the surf-rock “Galley Slave,” which sports some inarticulated vox humana.